Photocomposition is accomplished by projecting a series of images along a line of composition. The images are projected onto a photosensitive surface.
In the composition, the characters must be spaced from one another. The spacing varies according to assigned width values. Word spacing is a larger value than character spacing.
Spacing is accomplished by many differing means in various photocomposing machines. One very successful machines is the Comp/Set brand sold by Addressograph Multigraph Corporation of Cleveland, Ohio, U.S.A. U.S. Pat. No. 4,008,480 illustrates the lens and escapement system of that machine, wherein a mirror carriage is reciprocated by a stepper motor operation through a cable system.
The illustrations and teaching of U.S. Pat. No. 4,008,480 are incorporated by reference herein as if a part hereof. The structure of this prior patent was first used with a direct entry keyboard and did not operate at high speed. Hence there was no problem with the mirror being in ringing movement when a character is projected. The system simply uses a delay to allow any ringing to cease before character projection.
However, if the system is operated as a unit separate from a direct entry keyboard, such as under tape input, at a much greater speed, the system takes on an elastic characteristic.
Even though the drive cables are stable woven wire, and the carriage is very light in weight, speeds of 80 lines per minute as required in faster operation, will magnify the inertia and elastic nature of the system.
Ringing is a term which signifies the settling characteristic of the carriage. After attaining speed, the carriage inertia will cause the cables to stretch and retract when the the drive is stopped. The continued inertial carriage movement will then cause rebound. On an oscilloscope the forward and reverse movement appears as a diminishing wave form similar to the accoustical wave form of a bell.